1. Field of the Invention
The present invention relates to an oil channel structure for an automatic transmission, specifically an oil channel structure for supplying operating oil to a hydraulic actuator for forward clutch or exhausting oil from the hydraulic actuator, the oil channel structure being formed in a casing.
2. Description of the Prior Art
Recently, the present applicant proposed an automatic transmission wherein a plurality of clutches are provided to connect a certain rotating element of a planetary gear unit to an input shaft, and arranged in a unit in a rear casing of the automatic transmission end section.
The automatic transmission has an inner drum slidably connected to the input shaft in a boss section formed in the rear casing, and an outer drum is secured to the inner drum to form a clutch drum. A first movable member is fitted into the clutch drum to form a hydraulic actuator for operating the first clutch (forward clutch), and a second movable member is fitted into the first movable member to form a hydraulic actuator for operating the second clutch (reverse and direct clutch).
Hydraulic presure from the valve body is sent to a sector (arcuate) shaped indented section and annular indented groove through an oil channel formed in the rear cover, and supplied to each hydraulic actuator through an oil hole formed in the inner drum slidably connected to the boss section.
However, more than one oil channel and sector shaped indented section can not be made in each hydraulic actuator. The flow resistance of the oil channel per se is large and becomes an orifice, and the sector shaped indented section of the boss section is not well in alignment with the oil hole depending on the sliding position with respect to the boss section of the inner drum, which also makes an orifice structure.
Particularly, when the shift lever is moved from the D range to the N range to release the first clutch, on the basis of the return spring, oil which is forced out from the hydraulic actuator for the first clutch is subjected to the orifice of the oil channel formed in the rear casing and to the orifice of the oil hole formed in the annular indented groove and the inner drum.
Consequently, it sometimes requires a long time to release the first clutch from the N range shift of the shift lever. Consequently, after the N range shift, a driving force is continuously transmitted for a while, so that the creep running is continued long against the driver's intension. Further, when the shift to the N range is erroneously made during driving, the driving force is transmitted for a while, which causes a misunderstanding that the D range driving is still being continued followed by the sudden loss of driving.